Method of making vibration and sound damping materials



Jam 23, 1941. E. A. WORM, JR 2,229,4W1

METHOD OF MAKING VIBRATION AND SOUND DAMPING MATERIALS Filed March 20, 1940" Patented Jan. 21, 1941 UNITED STATES METHOD OF MAKING VIBRATION AND SOUND DAMPING MATERIALS Erwin A. Worm, Jr., Pensacola, Fla., assignor to Armstrong- Cork Company, Lancaster, Pa., a corporation of Pennsylvania Application March 20, 1940, Serial No.- 325,059

10 Claims.

This application is a Continuation in part of my application filed August 3, 1937, Serial No. 157,161.

This invention relates to a method of treat- 6 ing felted fibrous webs and finds particular usefulness in thefmanufacture of vibration damping and sound absorbing materials. The treated web will of course be useful for other purposes where the characteristics imparted to the Web by 10 the treatment may be found desirable.

Felt and felted products, with or without waterproofing or binders, have been used as sound damping and sound absorbing agents in connection with vlbratile metal sound producing and 16 transmitting surfaces, such for example as file cabinets, Office furniture, vehicular and automobile bodies, machinery pads, partition and wall constructions, and generally wherever a relatively cheap, easily applied material may ad- 20 vantageously be employed to reduce or inhibit the production or transmission of sound. Felt as produced by the usual water laying methods has not been entirely satisfactory for such uses in that the fibers of the water-laid sheet tend to 25 be predominantly oriented along the length of the sheet as produced on the machine, resulting in a polarizing of the flexibility characteristics'of the material, in which state, the material customarily produced exhibits its best flexing char- 80 acteristics in a direction along the length of the sheet, and its poorest flexing characteristics in a direction normal. to the length of the sheet. ,This non-uniform property is undesirable in the formation of vibration and sound damping and 85 absorbing materials intended to be conformed or applied to surfaces other than planar.

According to myinvention, a felted product, suitable for use as a vibration and sound damping and. absorbing material, is produced with a 40 high degree of uniformity with respect to'its flexing properties and in a much softer, less 1 boardy, condition than is customarily available Y in unindented and non-corrugated sheets.

As an example of my invention, I produce a 45 felted fibrous sheet which is preferably predomi-' nantly rag fiber, on a paper machine, which felt when dried and finished the usual way is in the neighborhood of thick and of the order of 1%; pounds per square yard, being somewhat 60 less dense than roofing felt. This sheet is rendered water resistant by the addition of asphalt or flux oil in such amounts "that the voids of the sheet are not completely filled, as, for example, is commonly done in flooring felts.

ll After the asphalt or flux oil has cooled from the usual saturating temperatures, I treat the sheet as diagrammatically illustrated in the accompanying drawing in which a felt sheet 2 is fed across tensioning rolls 3 and 4 and a guide roll 5 to the nip of differentially driven rolls 6 3 and I, and thence through difierentially driven rolls 8 and 9,10 and II, and I2 and I3, to a windup indicated generally at M. Rolls 1-, 9, II and i3 are driven faster than rolls 6, 8, I0 and H with which they are respectively paired. A lubri- 10 cant is applied to the surface of rolls 7! and 9 by means of wicks l5 dipping into troughs 16 in which a suitable lubricant such as kerosene is maintained to the required level. As a result of this arrangement, the felt web 2 fol1ows the slower moving rolls 6, 8, I0 and I 2 and a slipresuits between the felt web 2 and the faster moving rolls I, 9, H and I3. I have found that the lubricant applied to the surface of the fast moving rolls by the wiclcs l5 does not prevent the 20 felt from following the slow moving rolls which succeed the lubricant application and press on the lubricated surface, but in the absence of the lubricant, the heat generated by the slip between the felt web and the fast moving rolls results in sticking and tearing of the felt when sufficient pressure and differentialspeed exists to .obtain the optimum effect. I have found that with a series of four pairs of rolls, as diagrammatically illustrated, the difference between the surface 80 speeds of the rolls in each set may be from 10% to 15% of the speed of the fastest pair ofrolls, and yield a satisfactory commercial product. The manipulation of the sheet is preferably done after the waterproofing ingredient, such as asphalt or fiux oil, has been put into the sheet, for the effect of such partial saturation is to bind the fibers at their points of contact to generally stiffen and strengthen the sheet and if the waterproofing ingredient is first put into the sheet the distortion and softening effected by the differential working treatment permanently characteriz'es the sheet after such treatment. If the sheet is treated to the differential working prior to saturation, or partial saturation, the softening effect is not as great and subsequent saturation or partial saturation locks the fibers to a relatively stiffer structure. Where the 'sheetis to be used as a base or body for fioor coverings or. the like, a lesser degree of softening is generally satisfactory, but, as with vibration damping and sound absorbing felts, the preferred procedure is to effect the softening after the waterproofing agent has been incorporated into-the web.

Each of the rolls 6,1, 8, 9, ML, [2 and I3 is driven in order to maintain the required differential in surface speed and the concomitant working of the sheet. It will be observed from the drawing that the under surface of the web 2 is first engaged by the-high speed roll 1; then the upper surface by the high speed rolls 9 and II and finally the under surface is reeng'aged by high speed roll l3 to effect the final working. Thus eachfiat surface of the web is independently engaged so that mechanical working of one surface of the sheet is effected in one position and working of the other surface of the sheet, while effected simultaneously, is effected on a longitudinally spaced portion of the web, as distinguished from the action obtainable by feeding a web through a pair of rolls operating at a materially lower surface speed than the speed of travel of the web therethrough.

I prefer to employ smooth faced rolls so that the final sheet exhibits a plane face. My differential working treatment results in opening of the sheet, and the formation of pores, as well as the further opening of pores present in the unsaturated sheet, so that the finished treated material presents a surface requiring a minimum amount of adhesive to secure it to a surface to be treated, possesses pores for the escape of solvents of such adhesive, if the adhesive be of the solvent type, and, although waterproof, is nevertheless substantially symmetrically flexible and possessed or enhanced vibration and sound absorbing qualities.

It will be apparent that with other types of felts and other calipers and densities of sheets, other degrees of differential working may be employed with good results, but in no event should the treatment be carried to the point where the homogeneity and essential strength of the sheet are destroyed. all

My invention is particularly useful in connection with the treatment of vehicular bodies in which the application must be convenient and rapid and the treating material must be possessed of a high degree of ability to conform to angular and rounded surfaces. The fiexibilizing effect of the differential stretching and working, without defacing, indenting or corrugating the sheet, resuits in a superior vibratile damping and sound absorbing material requiring a minimum of adhesive for complete bonding to the surface to be treated.

The reason for the softening effect obtained by the treatment I have described is not entirely clear. I have found that the sheet is not materially increased inlength or Width, so that the effect is apparently not due to a permanent stretching of the sheet as a whole. I have also found that the flexlbilizing effect is enhanced by increased pressure between the rolls, although high pressure alone does not give the desired effect, and has the undesirable effect of permanently reducing the thickness of the sheet resulting in a more dense product with decreased vibratile vibration damping and sound absorbing propertles. The degree of pressure which I prefer maintained between the rolls is such that the felt is firmly pressed in the nip of the rolls but the thickness of the sheet is not permanently decreased more than in the neighborhood of 5% or 6% of its thickness before treatment. I believe that the softening effect is due to a crowding of the felt by each of the higher speed rolls into a nip through which it can travel only at the speed of the complementary slower speed roll, resulting in an intense working of the felt. I do not wish to be limited to any particular theory of operation, for whatever action takes place in my treatment, the result is a surprising increase in the flexibility and conformability of the product, together with a material increase in the vibration damping and sound absorbing properties. Tests have also indicated that the susceptibility of the sheet to expand and contract upon absorption and release of moisture is materially reduced by this treatment. Reduction of this tendency is desirable in surface coverings where dimensional changes will cause buckling.

While I have illustrated and described the present preferred embodiment of my invention, it will be understood that it may be otherwise practiced and embodied within'the scope of the following claims.

I claim:

1. In the methodof making vibration damping material from a water laid, felted, fibrous sheet, exhibiting its best flexing characteristics in a direction along the length thereof and its poorest flexing characteristics in a direction normal to the length thereof, partially saturated with an impregnant which tends to increase the stiffness of the sheet, the steps comprising subjecting opposite faces of the sheet to a pressure normal to said faces and simultaneously subjecting the surface of one of said faces to a force parallel to the plane of such face to effect displacement of the fibers and expanding of the surface, and subjecting the surface of the other face at a longitudinally spaced point to a force .directed parallel to the plane thereof to effect similar displacement.

2. In the method of making vibration damping material from a water laid, felted, fibrous sheet,

3. In the method of treating a water laid,

felted, fibrous sheet, exhibiting its best flexing characteristics in a direction along the length thereof and its poorest flexing characteristics in a direction normal to the length thereof, the steps comprising partially saturating said sheet with a Water-resistant material which binds the fibers at their points of contact and tends to increase the stiffness of the sheet, and thereafter alternately stretching the surfaces of the sheet while maintaining said surfaces sub'stantially'planar to effect displacement of the fibers and expanding of the surface of the faces of said sheet.

4. In the method in accordance with claim 3 in which the stretching is done with differentially moving surfaces applied to opposite faces of the sheet at points spaced longitudinally of the-sheet with sufiicient pressure to effect the stretching and insuiilcient pressure to materially permanently deform the sheet and with tension applied to the sheet in the zone between said points of engagement.

5. The method of treating a water laid, felted, fibrous sheet, exhibiting its best flexing characteristics in a direction along the length thereof a speed substantially the same as the surface.

speed of the slower of said rotating surfaces to effect displacement of the fibers and expanding of the surface of the face of said sheet.

6. A method in accordance with claim 5 in which the face in engagement with the slower moving surface is engaged by a subsequent faster moving surface and the opposite face of the sheet is simultaneously engaged by a slower moving surface.

7. In the method of treating a water laid, felted, fibrous sheet, exhibiting its best flexing characteristics in a direction along the length thereof and its poorest flexing characteristics in a direction normal to the length thereof, the steps comprising partially impregnating said sheet with a melted water-resistant material which binds the fibers at their points of contact and tends to increase the stiffness of the sheet, cooling said sheet and thereafter stretching the surface of said sheet to effect displacement of the fibers and expanding of the surface thereof to render the same substantially more flexible in a direction normal to its length than the original partially impregnated sheet.

8. A method in accordance with claim 5 in which lubricating material is applied to the working area of the faster rotating surface.

9. In the method of making a vibration damping material from a water laid, felted, fibrous web, exhibiting its best flexing characteristics in a direction along the length thereof and its poorest flexing characteristics in a direction normal to the length thereof; partially saturated with an impregnating medium disposed within the body thereof but not completely saturating the same. which impregnant tends to increase the stiffness of the web, the steps comprising feeding such web to a pair of differentially rotating rolls, compressing the material between the rolls while moving the web therebetween at a speed substantially the same as the surface speed of one of said rolls, the other of said rolls rotating at a speed materially in excess of the rate of travel of said web between the rolls, engaging the surfaces with a second pair of differentially rotating rolls and compressing the web therebetween while moving ,the same therethrough, the surface speed of the roll in engagement with the surface previously engaged by the high speed roll being substantially the same as the surface speed of the material moving through said pair of rolls, whereby the opposite faces of said web are stretched and expanded without materially increasing the length of the web and a webhaving a high degree of uniformity with respect to its flexing properties is produced.

10. A method in accordance with claim 1 in which the sheet is pressed between oppositely disposed driven rolls and the rolls are rotated at different speeds.

' V ERWIN A. WORM, JR. 

